Carbon Nanotube Film Anodes for Flexible Li-Ion Batteries

Abstract

In these days, IT devices such as smart card, flexible display and wearable devices requires flexible and high performances. To satisfy these demands, the battery also must be flexible and have high energy density. Lithium ion batteries(LIBs) with high energy density and long cycle performance are most promising candidate for wearable devices. However, the current collector which made of metal(Cu, Al) is an obstacle to flexibility of LIBs. For these reasons, many researches that replace metal current collector with flexible current collector had conducted. Nanocarbon materials such as carbon nanotube(CNT) and graphene have much attentions for using current collector of LIBs due to their high electrical conductivity. In addition, CNT and graphene also can perform as anode material of LIBs. Although nanocarbon materials have many advantages, they are suffered for the huge irreversible capacity and low coulombic efficiency at the initial cycling. This phenomenon is usually because of the formation of unstable solid electrolyte interface(SEI) due to nanocarbon materials’ large surface area. In this study, we tried to improve LIB’s reversible capacity and coulombic efficiency by forming stable SEI on CNT film’s surface. The CNT films were synthesized via direct spinning method. Stable SEI was formed by directly contacting CNT film with Li metal in electrolyte (1M LiPF6 solution in ethyl carbonate(EC) and diethyl carbonate(DEC) (1:1 v/v)) for 1h before cell assembled. The prelithiated CNT film was assembled to coin type half-cell without polymer binder and current collector under argon environment. According to the electrochemical analysis of the cells, directly prelithiated CNT film electrode didn’t show the SEI peak in the CV curve and very low surface resistance was measured in impedance test. After stabilization of a few initial cycles, the capacity increased up to 1300mAh/g at 300th cycle, which was higher than theoretical capacity of CNT. Pouch type cell assembled with the prelithiated CNT film was normally worked and maintained stable OCV during crumpled.